REMOVING BROKEN TAP

[lancelot]

Hello folks,
I know I have seen in among all this information, something about removing the broken bit of a tap from a GUNMETAL casting. I think someone mentioned ''ALUM'', what is the proper chemical name for it and how does it work? it's a 7 ba intermediate with 1/4'' buried in the casting
All help greatly appreciated,
All the best for now,
John.

[ridleyian]

Hi John
Get some alum (potash alum used for bed sores!)
Make a close to saturated solution and immerse your casting in it. If you can contrive some sort of double boiler to keep the solution close to boiling then it will work in just a few hours.
You will see bubbles rising from the broken tap as it turns into a black paste (some sort of ferric compound presumably) Mechanical agitation helps as does a bit of judicious poking to clear out the black gunge.
I of course never break taps-Much!
Hope this helps
Ian

[lancelot]

Hello Ian,
thank you for replying, I will ask our local Chemist if they have any and if not where I can obtain it.
All the best for now,
John.

[lancelot]

Hello folks,
with reference to the above and obtaining ''ALUM'', I have approached all the Chemists in our area, to no avail. some even suggested Garden centres, the 'Potash' bit, one asked me what the process involved and when I described how it worked, he remarked '' in the old days, you would have been burned at the stake, it's only Witches and Warlocks who did that! '' must have been the Hubble Bubble bit in the Cauldron, that did it.
Anyway, to be serious, has anyone the address for a supplier [in small quantities] of 'ALUM' or as I think it is known as ALUMINIUM POTASSIUM SULPHATE, as in my part of the country it would appear not to exist.
All the best for now,
john.

[the_viffer]

You can get alum from clockmakers suppliers eg HS Walsh (who are on the web). They will also sell you 50kg sacks of potassium cyanide

I think you can also get it from fishkeepers' suppliers who use it for getting the turbidity out of water.

You could try craft shops which cater for paper making as it is used in sizing hand made paper.

Potash and potassium sulphate are not alum. Neither is aluminium sulphate. Potassium aluminium sulphate and aluminium potassium sulphate are alum.

It is possible to make it from potassium sulphate and aluminium sulphate. I'm too lazy to do the calculation on proportions now but will gladly do it if needed.

It is rather fun to make yourself from an old soft drinks can. You dissolve the can in some potassium hydroxide (sodium hydroxide will do at a pinch to make soda alum). Then you neutralise with sulphuric acid and then boil off the water. It is a rather good test for budidng chemists since everyone should get the same amount of product from a can. Some get too much because their product is impure and some get too little because they have been inefficient in handling the material. You do need a chemical balance to weigh out the reagants so maybe not the job for everyone!

[lancelot]

Hello the_viffer,
brilliant, just obtained 500gms. from Walsh and they can post it too....
Thank you very much for the help,
All the best for now,
John.

[the_viffer]

I'm glad if I helped.

Cheers!

[lancelot]

Hello Folks,
to continue the saga of ''the broken Tap'', after the collective brain picking of this Forum and others, one in particular [the american horological society], the final result was to remove it with the use of ''ALUM'' i/e...aluminium potassium sulphate...this chemical is commonly used in the clock repair trade for removing rusted or broken screws from out of rare or antique clocks or watches when all else fails.
The process is slow but very sure as I have just proved.
During the tapping of a considerable number of 7ba threads, I managed to snap the Tap leaving approximately 3/8'' of broken tap in a blind hole.
The removal of the broken piece involved the use of a large sauce pan, a pyrex bowl, and 'ALUM', the pyrex bowl was filled with boiling water enough to cover the cylinder with broken tap by about 2'' of liquid, 'ALUM' powder was then poured into the bowl of boiling water until no more powder could be absorbed by the water, the bowl of liquid 'ALUM' was then put into the large saucepan which already had boiling water in it and left to simmer at just under boiling point for 15 hours over yesterday and today, that is what I mean by 'slow but sure', the gunmetal casting was not affected in any way and the remains of the broken tap had vanished.
It was amazing to watch the constant stream of tiny little bubbles erupting from hole where the broken bit of tap was being eaten away with the chemical.
For anyone who has never used this process before [like myself] I would heartily endorse it as an excellent ''MODEL ENGINEERS '' tool.
All the best for now,
John.

[ridleyian]

I don't normally say very much, but just for once.....told you so!
Back to lurking
Ian

[Roger Mason]

Hi John,

It was really good to read of your success in removing your broken tap. I have filed your description of the process away for future reference.

To make the description complete could you give some guidance as to how much alum will dissolve in say a pint of water? Could the solution be kept for further use in the future (you can see I am a pessimist!)? I assume you bought your supply from Walsh, or some other clock/watch supply house - any guidance on the sort of price we are talking about?

Lets hope I don't need to use any of this information, but armed with it a disaster could be turned into a rescued casting.


Cheers,


Roger Mason, in St. Agnes.

[the_viffer]

Roger

I'm going to let John answer the price question (which I think is quite a lot but less than buying a new casting)

I can asnwer your other questions

Solubility

deg C g/100g water

0 5.7
10 8.5
20 12
30 18.5
40 25
50 36.8
60 58.5
70 94.4
80 195

So it depends a lot on temperature. It also means you can have fun making crystals with it while waiting to dissolve a tap.

I think it is indefinitely stable in solution.


John could you do a small experiment for me sometime? Could you see if alum dissolves ferrous in the absence of gunmetal?

The boss and I are trying to work out why it works. One possibility is that it forms a battery with the iron and the gunmetal each forming an electrode. Take away the gunmetal and it stops working would be evidence that it is electrochemical.

Cheers!

[the_viffer]

I've just found www.crystalgrowing.com/index_e.htm offer 1000g of potassium alum for Euro6.40 plus shipping. Maybe be cheaper than HS Walsh. I've no connection with the website and have never used them. I have used HS Walsh (I live round the corner from them) but have no connection with them. They have never let me down.

[lancelot]

Hello Roger,
The price from Walsh including postage to Northern Ireland for 500gms.was £19.00, well worth the price, as I used only about 200 gms in 3/4 pint to remove it. I dare say I could have kept the Alum liquid for future use , but I binned it as it appeared rather murky.
The_viffer, if I get a chance I will run that little experiment, just to see what happens.
All the best for now,
John.

[JohnP]

Going back to the start of the thread, I'm suprised that The-viffer didn't suggest making alum the old fashioned way.

It was a big thing in North Yorkshire at one time after Henry VIII had his tiff with Rome and got our imports of Alum (from Italy) stopped.

You need some shale which you heat for about 3 months and large quantities of stale urine.

JohnP

[Roger Mason]

Hi All,

Thanks for the information that I asked about. I have carefully filed it away for future reference.

With regards to the way it used to be manufactured, I seem to remember seeing something about this on T.V. some time ago. I think it was used in the fabric dyeing process. The thing that amazed me is how did anyone actually discover that if you fired shale for three months and then...

What on earth could they have been doing to discover this?


Cheers,


Roger Mason, in St. Agnes.